Roasting coffee

Roasting coffee

To round off the week, we thought it only made sense to visit a topic we briefly mentioned on Thursday- roasting coffee. If you can excuse us our ducking backwards and forwards along the coffee making process, please join us as we see how the roast affects one of our top brews!

A load of hot air

First of all- why do we roast coffee? Whilst we won't pretend to understand the complex chemical reactions that take place (you can have a crack at it yourself if you follow this link!), the only thing that is really important to know at the moment is that it makes your coffee taste better.

When it comes to industrial scale roasting, there are two main ways it is done: drum and hot air. With drum machines, the beans are placed inside and then tumbled around whilst the drum is heated. It used to be that the beans were directly heated by a fire using the drum method, but that has fallen out of favour these days for indirect heat; no doubt you're less likely to spoil your beans this way. Hot air roasters use large beds to roast coffee. The bottom is a screen or perforated plate on which the beans lay, with hot air forced through underneath. This creates a fluidized bed, with the beans tumbling around on the jet of air. In both cases, they have ways of moving the beans around- this is important in order to achieve an even roast.

Roasting coffee isn't just confined to an industrial scale, however. Roasting at home is perfectly possible and can in fact be very simply done. The easiest way is to spread out a layer of beans on a baking tray and stick them in the oven. Another way is to roast them in a pan on the stove- this one has the added benefit of being able to see how they're doing! A slightly more advanced method, if only by dint of needing a more specialized bit of kit, is to roast them in a popcorn machine. This is the recommended home roast method, as it is easiest to achieve an even roast with it.

Bitter or sweet

So how does roasting affect taste? It seems you can generalise it with a few sliding scales, namely things like acidity, sweetness, bitterness and 'greenness'. At the lightly roasted end, acidity and greenness come through strongly. The sugars are unlikely to be at play yet, as they haven't had time to caramelize. As you move through to the mid range, the greenness disappears and the acidity slowly drops off. The sweetness starts to come in to play too. As you reach the highly fired end- which stops just short of charcoal- the acidity is eventually all but removed. The sweetness transforms into bitterness as the sugars begin to burn, and the flavour of the coffee itself is dominated instead by the roast- perfect if you're a fan of lapsang souchong!

As before, if you'd like to examine the process in more detail be sure to check out the references below.